i use one of these controllers. the only time i've had spike was just after i put the front mount on and had the controller receiving its reading from the bov hose. took the nipple off the old cooler piping and put it onto the pipe from the turbo to the cooler and the spiking went away.
i have an rb25 and i'm running 14psi on the stock turbo (yes i know you shouldn't run them above 12, but it goes much better, and when it goes i have an excuse to get a bigger turbo). i don't get any spiking, but i do have bleed off at high rpm at WOT, but i have put this down to the turbo maxing out rather than the controller.
and i'm about to take the controller off to go to an even cheaper setup that should be more reliable again, as it won't be leaking air out of the system at all.
i can't see the point in spending hundreds off dollars on a boost controller that most people won't notice any more power from.
as for how a controller can make boost build earlier, as the boost builds the wastegate starts to creep open and is fully open by the pressure it is set to. when you put a controller like the turbotech in, its design stops prssure getting to the wastegate until a higher level, so the boost has already started builing when the wastegate starts to open.